B-2: Least mission-ready. (Staff Sgt. Nick Wilson/Air Force)

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The Air Force’s most expensive plane, the $1-billion-per-copy B-2 Spirit stealth bomber, is regularly the service’s least mission ready. It sees a break rate of 24.2 percent. However, it is a small fleet, which figures into its statistics, and crews are able to turn the bombers around at a high rate: 57.7, the highest of the service’s bomber fleet. The B-2 has seen activity in all recent conflicts, showing that maintainers are able to keep it ready when needed, said Maj. Michael Bradley with Air Force Global Strike Command’s B-2 weapons system team.

“This smaller B-2 fleet has a low demand for parts; that in turn creates an industrial base support problem as many of the small original equipment manufacturers are no longer able to supply those parts,” said Senior Master Sergeant Virgil Tims, with Global Strike’s B-52 weapons system team.

B-2s head to depot maintenance for a full overhaul every seven years, taking the bomber out of the rotation for the full 13-month maintenance cycle.However, officials are planning a different depot cycle to keep more B-2s available, sending the B-2 in for a short tuneup every five years and a complete overhaul every 10. In fiscal 2013, 26 percent of the fleet was in depot maintenance.

The B-52 Stratofortress, one of the service’s oldest airframes at an average age of 51.7 years, keeps a high break rate, 36.4 percent, but those bombers are turned around at a rate of 35.6 percent, the lowest of the service’s three bombers.

B-52s head to depot maintenance at a regular 48- to 51-month cycle. The depot maintenance tasks are annually reviewed to identify and correct discrepancies that field maintainers cannot repair, Tims said.

The non-nuclear B-1B Lancer breaks the least, at a rate of 22.1 percent in fiscal 2013, and crews are able to fix 39.3 percent in 12 hours, according to Air Force statistics.